This invention relates to techniques for testing earth samples and, more particularly, to an apparatus and method for measuring volatile constituents in a sample of ground water or soil mixed with water. The invention was supported by the U.S. Environmental Protection Agency, and the U.S. Government has certain rights in the invention.
The leakage of underground storage tanks, and other types of pollution which introduce hydrocarbons and other volatile contaminants into the ground, has become a serious problem in many places. Recent federal, state and local regulations have or will soon require that investigations be conducted to determine whether underground gasoline storage tanks have leaked. An integral part of these investigations is determining whether soil or ground water in the vicinity of tanks have been contaminated. This is generally accomplished by the use of soil/gas surveying, drilling to collect soil samples, and construction of monitoring wells to collect ground water samples. Of significance are the more soluble and easier to detect components of gasoline, such as benzene, toluene, ethylbenzene and the xylenes. Samples are generally analyzed in the laboratory by gas chromatography or gas chromatography/mass spectrometry for volatiles and semi-volatiles using a number of known methods. Given the relatively high costs for these analyses, field screening can be conducted to select samples for laboratory evaluation. Also, field screening is used to guide investigations in terms of the depth and lateral extent of drilling. Additionally, field screening may be employed in guiding remediation by excavation. An evaluation of some existing field screening techniques, particularly those using so-called "headspace sampling", are described in "Use Of Headspace Sampling Techniques In The Field To Quantify Levels Of Gasoline Contamination In Soil And Ground Water", G. A. Robbins et al., Proc. of NWWA/API, Nov. 1987.
Headspace sampling techniques involve placing a consistent volume or weight of ground water or soil mixed with water in a container, sealing the container, agitating, allowing time to permit volatile constituents to be released into the air headspace of the container, and then using a detector to measure the volatile constituent in the headspace. Existing headspace sampling techniques have various disadvantages and limitations, and it is among the objects of the invention to provide an improved headspace sampling apparatus and method.